With the rapid development in renewable energies as a trend in recent years, the interface between the renewable energies and AC utility has attracted tremendous attention. Distributed power systems having DC-to-AC inverters use active switches such as IGBT's, ESBT's, SiC-SBD's, SiC-JFET's and SiC-SIT's to achieve miniaturization and high conversion efficiency by high-frequency switching. However, parasitic inductance and parasitic capacitance may occur at high frequencies to result in significant electro-magnetic interference and RF interference that may adversely affect the performances of electronic products or even cause damages to electronic products.
The high-frequency pulse-width modulation (PWM) power conversion system using soft switching exhibits lowered switching loss, reduced electro-magnetic interference and RF interference and higher power densities.
DC-to-AC inverters are mostly used in distributed power systems or renewable energy systems to convert DC power to AC power. The active switches with hard switching in the inverter often result in switching loss, such as turn-on loss or turn-off loss. Moreover, with hard switching, surge voltage often occurs to damage the switches. If the switching loss can be lowered, the conversion efficiency of the DC-to-AC inverter can be enhanced and so is the lifetime of the switches. As the switching frequency increases, parasitic inductance and parasitic capacitance may occur to result in significant electro-magnetic interference and RF interference. On the contrary, soft switching may help to achieve zero-voltage or zero-current switching to solve problems due to electro-magnetic interference and RF interference.
The conventional DC-to-AC inverter uses hard switching to cause significant electro-magnetic interference and RF interference due to parasitic inductance and parasitic capacitance. Therefore, there is need in providing a resonance circuit using zero-voltage switching to reduce switching loss, enhance conversion efficiency and eliminate electro-magnetic interference as well as the RF interference due to dynamic transient changes of the voltage (dv/dt) and of the current (di/dt).